Apparatus for acoustic-emission inspection of articles

ABSTRACT

The apparatus for acoustic-emission inspection of articles has channels  e including a series connection of a transducer of acoustic emission signals, positionable on an article under inspection, and an amplifier of electric signals, having connected to its output a unit for measuring the parameters of acoustic emission signals and a shaper of single pulses, of which the output is connected to the first input of a unit for measuring time intervals. The other input of the unit for measuring time intervals of each channel is connected to the output of a clock pulse generator. The output of the clock pulse generator is also connected to the input of a frequency divider. The apparatus further comprises an OR gate of which the inputs, in a number equalling the number of the channels, are connected to the outputs of the shapers of single pulses of each channel, and the output is connected to the third inputs of the units for measuring time intervals in each channel. The outputs of the units for measuring the parameters of acoustic emission signals and of the units for measuring time intervals of each channel are connected to the inputs of a switching device. A computer for processing acoustic emission data is connected to the switching device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to apparatus for nondestructive inspectionand testing of articles, and more particularly it relates to apparatusfor acoustic-emission inspection of articles.

2. Description of the Related Art

There is widely known an apparatus for acoustic-emission determinationof the coordinates of a developing crack in an article, comprising aplurality of channels each including a serial connection of a transducerof acoustic emission signals, positionable on an article, underinspection, and an amplifier of signals of acoustic emission. Theoutputs of the amplifiers of acoustic emission signals of all channelsare connected to the first inputs of an encoder. Connected to the firstoutputs of the encoder are the first inputs of respective shiftregisters in a number equalling the number of the channels. The outputsof all shift registers are connected to the inputs of the first OR gateand to the first input of an electronic computing unit having its outputconnected to the input of a registration unit. The output of the firstOR gate is connected to the respective first inputs of the first andsecond flip-flops. The first output of the first flip-flop is connectedto the second input of the encoder. The second output of the firstflip-flop is connected to the first input of a counter. The apparatusfurther comprises a second OR gate of which the first input is connectedto the second output of the electronic computing unit, the second inputis connected to the first output of the counter, and the output isconnected to the second inputs of the respective shift registers, to thesecond input of the first flip-flop, and to the first input of the thirdOR gate. The second input of the third OR gate is connected to the thirdoutput of the electronic computing unit. The output of the third OR gateis connected to the second input of the second flip-flop.

The apparatus also comprises a series connection of a clock pulsegenerator and an AND gate, the second input of the electronic computingunit being connected to the output of the second flip-flop, as is thesecond input of the AND gate, and the third input of the electroniccomputing unit being connected to the digit outputs of the counter. Thethird inputs of the shift registers are connected along with the secondinput of the counter, to the output of the AND gate.

When a developing crack evolves in the article, a signal comes to thetransducer of acoustic emission signals, and the code of the channelwhich has been the first to receive the acoustic emission signal iswritten in the lower-order digits of the shift registers. Then this codeis shifted in the shift registers through the number of digit positionscorresponding to the time interval passing before the instant ofreception of an acoustic emission signal by another channel, whose codeis written in the lower-order digits of the shift registers.

The appearance of the code of the first-mentioned channel at the outputof the registers triggers the process of data transfer to the electroniccomputing unit. The counter counts the number of the digit positionsbetween successive codes written in the shift registers, thusdetermining the time intervals between the instants of reception of theacoustic emission signals in the respective channels. However, for theapparatus to ensure proper functioning of this data-reading mode, theencoder is inhibited, so that reception of new information is alsoinhibited. This amounts to a high probability of useful signals ofacoustic emission being missed by the apparatus, which significantlyimpairs the reliability and credibility of the inspection of an article.

Also widely known is an apparatus for determining from acoustic emissionsignals the coordinates of a crack developing in an article, comprisinga plurality of channels each including a series connection of atransducer of acoustic emission signals positionable on an article underinspection and an amplifier of electric signals having its outputconnected to the respective inputs of a shaper of single pulses and of aunit measuring the parameters of acoustic emission signals. The outputsof the shaper of single pulses and of the unit measuring the parametersof acoustic emission signals are connected to the first and secondinputs of the register of the channel. The apparatus further comprises aseries connection of a clock pulse generator and a pulse counter havingits output connected to the third inputs of the registers of therespective channels. The channels are arranged in groups, the outputs ofthe registers in each group being united by a common bus serving as aswitching device and being connected to the input of a primary dataprocessing unit corresponding to this group. The outputs of the primarydata processing units are united by the second common bus and connectedto the input of a computer having its output connected to the input of aregistration unit.

When a developing crack evolves in the article under inspection, and anacoustic emission signal reaches the channel which is the first toreceive this signal, the current time from the commencing of theinspection operation, monitored by the counter, is written into theregister of this channel. At the same moment, the register has recordedtherein the outcome of the measurement of the parameters of the acousticemission signal (i.e. its amplitude and duration), and this informationis fed to the computer via the switching device. As soon as otherchannels receive the signal, they also feed their information to thecomputer. The computer calculates the time intervals between theinstants of reception of the acoustic emission signals, computes thecoordinates of the source of acoustic emission in the article andassesses its potential hazard.

However, this apparatus would not ensure sufficient reliability andcredibility when articles with a high level of inherent activity areinspected. This is explained by the insufficient throughput of thecomputer which has to handle coded words of an extended size in theappratus being described. To ensure adequate accuracy of computation oftime intervals between the instants of reception of acoustic emissionsignals, the current time should be counted in increments as small asmicroseconds, and in some cases even as small as fractions ofmicroseconds. However, the maximum value of the current time can bedozens of minutes, hours or even days, depending on the kind of thearticle under inspection and the test conditions. Thus, the length ofcoded words representing the current time at the input of the computercan be from 30 to 40 bits, whereas the standard word length ofpresent-day computers is generally from 8 to 16 bits. In other words,the computer of the apparatus being described is doomed to operation(i.e. input, intermediate handling, computation) with words whose lengthis several times over the standard word length it is rated for. Theconsequence of the low throughput of the computer can be the loss ofacoustic emission information, which, in its turn, affects thereliability and significance of the inspection of an article. Moreover,the apparatus of the prior art being described has an excessive amountof electric connections between its measuring and processing parts,which steps up the noise protection requirements and complicates thedesigning of the apparatus.

SUMMARY OF THE INVENTION

The problem is solved by an apparatus for acousticemission inspection ofarticles, comprising channels each including a series connection of atransducer of acoustic emission signals positionable on an article underinspection, and an amplifier of electric signals having connected to itsoutput a shaper of single pulses and a unit measuring the parameters ofacoustic emission signals, and also a clock pulse generator connectedwith each channel, a switching unit having its inputs connected to theoutputs of the units measuring the parameters of acoustic emissionsignals and also connected with the shapers of single pulses of therespective channels, and a computer for processing acoustic-emissiondata, connected to the switching unit, which apparatus, in accordancewith the present invention, further includes in each channel a unit formeasuring time intervals, having its first input connected to the outputof the shaper of single pulses, its second input connected to the outputof the clock pulse generator, and its output connected to the input ofthe switching unit, and also a frequency divider having its inputconnected to the output of the clock pulse generator and its outputconnected to the switching unit, and an OR gate whose inputs in a numberequalling the number of the channels are connected to the respectiveoutputs of the shapers of single pulses of each channel, and whoseoutput is connected to the third inputs of the respective units formeasuring time intervals in each channel.

To enhance still further the reliability of the inspection of articles,it is expedient that the apparatus should comprise an additional unitfor measuring time intervals, having its first input connected to theoutput of the frequency divider and to an additional input of the ORgate, its second input connected to the output of the clock pulsegenerator, its third input connected to the output of the OR gate, andits output connected to the input of the switching unit.

The disclosed apparatus for acoustic-emission inspection of articlesprovides for measuring time intervals between the instant of receptionof an acoustic emission signal by the transducer of acoustic emissionsignals of one channel and the instant of reception of the acousticemission signal by the transducer of acoustic emission signals ofanother channel, without measuring the current or running time of thereception of each acoustic emission signal, which significantly reducesthe length of the coded words at the input of the computer and minimizesthe processing time of each acoustic emission signal evolving in thearticle. In this way the throughput of the measuring part of theapparatus is stepped up, the loss of acoustic-emission data in theinspection of articles with high levels of acoustic emission activity iscurtailed, and the reliability of the inspection of such articles isenhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described in connection with itsembodiments in an apparatus for acoustic-emission inspection ofarticles, with reference being made to the accompanying drawings,wherein:

FIG. 1 is a block unit diagram of one embodiment of the apparatusaccording to the invention;

FIG. 2 is a block unit diagram of the shaper of single pulses in theapparatus embodying the invention;

FIG. 3 is a block unit diagram of the unit for measuring time intervalsin the apparatus embodying the invention;

FIG. 4 is a block unit diagram of the unit measuring the parameters ofacoustic emission signals in the apparatus embodying the invention;

FIG. 5 is the block unit diagram of another embodiment of the apparatusaccording to the invention;

FIG. 6 is a chart plotting the voltage versus time at the components ofthe apparatus embodying the invention;

FIG. 7 is a chart plotting the voltage versus time at the components ofthe unit measuring the parameters of acoustic emission signals in theapparatus embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus for acoustic-emission inspection of articles comprises aplurality of measurement channels 1 (FIG. 1) in a number dependent onthe surface area of the article under inspection, the required accuracyof locating a source of acoustic emission, the expected level ofacoustic emission signals in an article, and the attenuation factor ofacoustic emission signals in the article. The minimum number of thechannels is three, which is defined by the number of measurementsnecessary for solving the triangulation problem in locating a source ofacoustic emission. Each channel 1 includes a series connection of atransducer 2 of acoustic emission signals, an amplifier 3 of electricsignals, a shaper 4 of single pulses and a unit 5 for measuring timeintervals. The output of the amplifier 3 of electric pulses is connectedto the first input of the shaper 4 of single pulses. The output of theshaper 4 of single pulses is connected to the first input of the unit 5for measuring time intervals.

The output of the amplifier 3 of electric signals has also connected toit the first input of a unit 6 measuring the parameters of signals ofacoustic emission.

The piezoelectric transducer 2 of acoustic emission signals of agenerally known structure (Greshnikov V.A., Drobot Yu. B."Akusticheskaya emissiya", 1976, Izdatel'stvo Standartov/Moscow/, pp.71-76) is fastened to the surface of an article under inspection with anacoustically transparent adhesive, a strapping, a permanent magnet (forarticles of ferromagnetic materials), or any other means ensuringreliable acoustic contact with the surface of the inspected article.

The amplifier 3 of electric signal is likewise of a generally knownstructure (Greshnikov V.A., Drobot Yu. B. "Akusticheskaya emissiya",1976, Isdatel'stvo Standartov /Moscow/, pp. 76-78).

The outputs of the unit 5 for measuring time intervals and of a unit 6for measuring the parameters of acoustic emission signals are connectedto the inputs of a switching unit 7. The outputs of the switching unit 7are connected to a computer 8 for processing acoustic-emission data.

The computer 8 is an all-purpose electronic computer of any suitableknown structure.

The apparatus further comprises an OR gate 9 having its inputs 10 in anumber equalling the number of the channels 1 connected to the outputsof the respective shapers 4 of single pulses.

The apparatus still further comprises a clock pulse generator 11 havingits output connected to the respective second inputs of the shapers 4 ofsingle pulses, the second inputs of the time interval measuring units 5of the respective channels 1, and to the input of a frequency divider12. The output of the frequency divider 12 is connected to the switchingunit 7.

The output of the OR gate 9 is connected to the respective third inputsof the time interval measuring units 5 of each respective channel 1.

The output of the computer 8 is connected to the respective fourthinputs of the time interval measuring units 5 and to the respectivesecond inputs of the units 6 for measuring the parameters of acousticemission signals.

The shaper 4 (FIG. 2) of single pulses includes an amplitudediscriminator 13 of which the first input 14 serves as the input of theshaper 4 of single pulses, connected to the output of the amplifier 3 ofelectric signals. The other input 15 of the shaper 4 is connected toreceive a discrimination threshold signal from a reference voltagesource 16. The output of the amplitude discriminator 13 is connected tothe reset input 17 of a counter 18 having its outputs connected to theinputs of a decoder 19. The shaper 4 of single pulses further includesan AND gate 20 having its first input 21 connected to receive clockpulses from the clock pulse generator 11, its second input 22 connectedto the output of a flip-flop 23, and the output connected to a countinginput 24 of the counter 18 and a first input of a flip-flop 25. Theinput 21 of the AND gate 20 is also connected to the input of a delayline 26. The flip-flop 23 has its first input connected to the output ofthe amplitude discriminator 13. Second inputs of the flip-flops 23 and25 are connected to the output of the decoder 19. The shaper 4 of singlepulses still further includes a flip-flop 27 having its first inputconnected to the output of the decoder 19 and its second input connectedto the output of a delay line 28. Respective outputs of the delay line26 and flip-flops 25, 27 are connected to the first, second and thirdinputs of an AND gate 29. The output 30 of the AND gate 29 is connectedto the input of the delay line 28 and serves as the output of the shaper4 of single pulses.

The unit 5 (FIG. 3) for measuring time intervals includes a flip-flop 31of which the first input 32 is connected to the first WRITE input 33 ofa register 34 and serves as the first input of the unit 5, connected tothe output of the shaper 4 of single pulses. The other input 35 of theflip-flop 31 is connected to the output of an AND gate 36 having itsfirst input 37 connected to receive a reset signal from the output ofthe computer 8. One output of the flip-flop 31 is connected to the firstinput 38 of an AND gate 39 and to the first input 40 of an AND gate 41.The other input 42 of the AND gate 39 serves as the second input of theunit 5, connected to the output of the clock pulse generator 11. Theoutputs of the AND gates 39, 41 are connected, respectively, to thecount input and reset input of a counter 43.

The unit 5 further includes a counter 44 having its count inputconnected to the output of a delay line 45. The output of the delay line45 is also connected to the second input 46 of the AND gate 41. Theinput 47 of the delay line 45 serves as the third input of the unit 5for measuring time intervals, connected to the output of the OR gate 9.

The output of the counter 44 is connected to the data input 48 of theregister 34. The output of the register 34 is connected to the firstinput of a comparison circuit 49. The second input of the comparisoncircuit 49 is connected to the output of a counter 50 having its inputconnected to the input 37 of the AND gate 36. The unit 5 still furtherincludes an AND gate 51 having its first input connected to the secondoutput of the flip-flop 31, its second input connected to the output ofthe comparison circuit 49, and its output connected to the input of anAND gate 52. The unit 5 also includes a channel number register 53. Theoutputs of the counter 43, of the AND gate 51 and of the channel numberregister 53 form the output 54 of the unit 5 for measuring timeintervals, connected to the input of the switching device 7.

The unit 6 (FIG. 4) for measuring the parameters of acoustic emissionsignals includes a video detector 55 of which the input 56 serves as theinput of the unit 6, connected to the output of the amplifier 3 ofelectric signals. The output of the video detector 55 is connected tothe input of a pulse shaper 57 and to the first input 58 of a peakdetector 59. The output of the pulse shaper 57 is connected to the firstinput 60 of an AND gate 61 having its second input 62 connected toreceive clock pulses from the clock pulse generator 11. The output ofthe AND gate 61 is connected to the count input 63 of a counter 64. Theoutput of the peak detector 59 is connected to the first measurementinput 65 of a voltage-to-code converter 66 of which the second controlinput 67 is connected to the ouput of the pulse shaper 57. The secondinput 68 of the peak detector 59, the third input 69 of thevoltage-to-code converter 66 and the second (reset) input 70 of thecounter 64 are connected to receive CLEAR signals from the computer 8.The output 71 of the counter 64 and the output of the voltage-to-codeconverter 66 form the output of the unit 6 for measuring parameters ofacoustic emission signals, connected to the input of the switching unit7.

The modified embodiment of the apparatus for acoustic-emissioninspection of articles, according to the present invention,schematically illustrated in FIG. 5 additionally comprises a unit 72(FIG. 5) for measuring time intervals, having its first input connectedto the output of the frequency divider 12 and to the additional input 73of the OR gate 9, its second input connected to the output of the clockpulse generator 11, and its third input connected to the output of theOR gate 9. The output of the unit 72 is connected to the switchingdevice 7. Structurally, the additional unit 72 for measuring timeintervals is similar to the unit 5 described hereinabove.

The disclosed apparatus for acoustic-emission inspection of articlesoperates, as follows.

The evolution and development of cracks and strained areas in thestructure of an article yield waves of acoustic emission responded to bythe transducers 2 (FIG. 1) fastened to the surface of the article, whichconvert them into electric signals (FIGS. 6 a, b, c) having theiramplitudes amplified by the amplifiers 3 in the respective channels 1.The parameters of these signals (i.e. the maximum amplitude andduration) are measured in the respective units 6 measuring theparameters of these signals of acoustic emission.

The video detector 55 (FIG. 4) of the unit 6 shapes the envelope of thesignal of acoustic emission (FIG. 7a). In measuring the duration of asignal, the pulse shaper 57 (FIG. 4) generates a signal of a presetamplitude (FIG. 7b) strobing the passage of clock pulses from the clockpulse generator 11 (FIG. 4) to the counter 64. Thus, the code value atthe output of the counter 64 is proportional to the duration of thesignal at the input of the measuring unit 6. The output signal of thevideo detector 55 is fed to the peak detector 59 which feeds out apotential (FIG. 7c) of a value equalling the maximum amplitude of itsinput signal. This signal is converted into a binary code by thevoltage-to-code converter 66 (FIG. 4), delivered jointly with the signalduration code to the output of the unit 6. The ensuing reset pulseresets the counter 64, the storage components of the voltage-to-codeconverter 66 and the peak detector 59.

The output of each amplifier 3 (FIG. 1) feeds out the acoustic emissionsignals also to the input of the shaper 4 of single pulses, intended torecover the acoustic emission signals against the background noise andto shape by their fronts the new pulses of preset duration and amplitude(FIGS. 6d, e, f). The presetting of the signals by amplitude isperformed by means of the amplitude discriminator 13 (FIG. 2) of theshaper 4, and the presetting of the signals by duration is performed bymeans of the digital components of the shaper 4 of single pulses.

In this, the pulses from the output of the amplitude discriminator 13set the counter 18 to "0" state, and the flip-flop 23 to "1" state. Thefirst clock pulse coming from the clock pulse generator 11 sets theflip-flop 25 to "1" state, and a clock pulse delayed by the delay line26 is produced at the output of the AND gate 29, setting, through thedelay line 28, the flip-flop 27 to "0", and thus inhibiting the passageof successive clock pulses to the input of the single pulse shaper 4.Then, the counter 18 counts the clock pulses, and if no pulse comes fromthe output of the amplitude discriminator 13 over a given period, thedecoder 19 reacts, setting the flip-flops 23 and 25 to "0" and theflip-flop 27 to "1". Alternatively, if pulses come during this givenperiod from the output of the amplitude discriminator 13, they reset thecounter 18 to start once again the counting of the required pausebetween the pulses.

The level of discrimination is set so as to recover useful acousticemission signals against background noise.

The time intervals Δt between pulses coming from the outputs of therespective single pulse shapers 4 of the individual channels 1 areconverted into binary code in the respective units 5 (FIG. 3) formeasuring time intervals, with each time interval Δt_(i) (FIG. 6h)beginning from the instant of reception of the preceding signal ofacoustic emission in either channel 1 (FIG. 1)--the output signal of theOR gate 9--and ending with the instant of reception of the next signalby this channel 1 (FIGS. 6d, e, f)--the signal at the output of thesingle pulse shaper 4. The time interval Δt_(i) (FIG. 6h) is measured bythe counter 43 (FIG. 3) by counting clock pulses coming to its input 42from the clock pulse generator 11. The counter 43 starts its up-countthe moment it is reset to "0" by a pulse coming from the output of theOR gate 9 to the input 47 of the delay line 45 of the unit 5.

The delay line 45 is intended to eliminate ambiguous situations causedby simultaneous application of pulses to the first input of the unit 5from the single pulse shaper 4 and to the third input of the unit 5 fromthe output of the OR agate 9. The counter 43 stops counting when theinput of the AND gate 39 receives a potential formed at the flip-flop 31receiving at its one input 32 a pulse from the output of the singlepulse shaper 4 and at its other input 35, via the AND gate 36, a resetpulse. Thus, a reset pulse is produced by the computer 8 when itreceives data from the channel 1 via the switching unit 7. Beside thevalue of the time interval, also delivered from the register 53 to theoutput of the unit 5 for measuring time intervals is the consecutivenumber of the channel 1 to which this unit 5 belongs.

Simultaneously with the reception of a pulse from the shaper 4 of singlepulses of the given channel 1, the code fed from the output of thecounter 44 which counts pulses received from the output of the OR gate 9is entered to the register 34. The counter 50 counts the successiveCLEAR pulses. When the codes (readings) of the register 34 and counter50 are the same, the comparison circuit 49 responds, and if theflip-flop 31 is in state "1", i.e. an acoustic emission signal has beenreceived by the given channel 1, there is formed a signal enablingtransfer of the data from this channel 1 via the switching unit 7 intothe computer 8. Thus, in the transmission of information from thechannels 1 to the computer 8, there is maintained the order in whichthese channels 1 have been receiving the signals of acoustic emission.This provides for the maximum efficiency and simplicity of the algorithmof computation in the computer 8 of the time intervals between signalscoming from different channels 1, which are necessary for calculatingthe coordinates of the source of acoustic emission.

The repetition rate (recurrence rate) of clock pulses is selected toensure the required accuracy of the counting of the time intervalsbetween signals of acoustic emission. The frequency divider 12 produces,from the recurrent pulses coming from the clock pulse generator 11, asequence of time marker signals (FIG. 6g).

A time marker signal is directly supplied to the switching device 7 and,further, to the computer 8. The time marker signals have a presetamplitude, their duration corresponding to the duration of the clockpulses like the duration of output pulses of the single pulse shaper 4).

As the time marker signal is not synchronized with the signals ofacoustic emission, the position of the last-mentioned signals in thecomputer 8 can be determined with the accuracy determined by theconsecutive number of a time marker.

In the embodiment of the disclosed apparatus shown in FIG. 5, a timemarker signal passes through the OR gate 9 to the third inputs of allthe units 5 and of the unit 72, and also to the first input of the unit72, initiating therein the same processes that are initiated in theunits 5 by the signals coming from respective single pulse shapers 4.

However, the additional unit 72 for measuring time intervals produces,not the channel number code, but a time marker indicator encoded with apredetermined numeral, e.g. "0". Thus, in the embodiment illustrated inFIG. 5 a time marker signal is introduced into the computer 8 via theswitching unit 7 in synchronism with the acoustic emission data. Withthe position of a time marker signal being fixed with respect either tothe last-received acoustic emission signal or to the preceding timemarker, and the position of the next-received acoustic emission signalbeing fixed with respect to this (current) time marker signal, therecurrence rate of the time marker signals is selected from anexpression: ##EQU1## where f_(t) is the recurrence rate (frequency) ofclock pulses; and

k is the digit (word) length of the time intervals measured in the units5 and 72.

This embodiment of the disclosed apparatus determines the time-relatedposition of each occurrence of acoustic emision with the accuracy of therecurrence period of clock pulses. Thus, in a prototype of the apparatusbeing described, the frequency of clock pulses is f_(t) ==1 MHz, and therecurrence rate of the time marker signals is f=16 Hz (the divider 12gives a 2¹⁶ :1 countdown). The information supplied to the computer 8includes the channel number code, the time marker indicating code, timeintervals Δt_(i) between the signals of acoustic emission and timemarkers, and the values of the parameters of the acoustic emissionsignals. The computer 8 computes time intervals between the signals ofacoustic emission, necessary for the computation of the coordinates oftheir sources, which is carried out by summing up the measured valuesΔt_(i), Δt_(i+1), Δt_(i+2), Δt_(i+3) (FIG. 6g).

Then the computer 8 calculates the coordinates of the sources ofacoustic emission. Thus, for a group of four transducers 2 arranged onthe article under inspection at the corners and center of an equilateraltriangle, the Cartesian coordinates of the source of acoustic emissionare computed from an expression: ##EQU2## where

    r.sub.j =Δt.sub.j V(j=1, 2, 3, 4);

where

Δt_(j) are the computed values of the time intervals with respect to thetransducer which has been the first to register the signal (for thistransducer, Δt equals zero);

V is the rate of propagation of acoustic emission signal in the articleunder inspection; and

B is the spacing of the transducers of acoustic emission signals.

Then the computer 8 calculates the energy characteristics of theaccoustic emission sources from a formula: ##EQU3## where S is thesuccessive number of the source;

l is the number of the occurrence of acoustic emission;

A is the maximum amplitude of the signal of acoustic emission, and

T is the duration of the signal of acoustic emission.

The values E_(s) thus computed are used to determine the potentialhazard from the S-th source of acoustic emission, e.g. from a developingcrack.

Thus, the employment of the present invention provides for enhancing thereliability of inspection of articles with high levels of acousticemission activity. The disclosed apparatus provides for determination ofthe time of occurrence of the acoustic emission phenomena with a highaccuracy, and thus for closely monitoring the dynamics ofacoustic-emission processes in an article under inspection.

The present invention can be employed in the oil-and-gas and chemicalindustries for quality control and inspection of major pipeline,compressor units, offshore stationary platforms; in nuclear powerengineering for testing and inspection of the reactors of nuclear powerplants; in aircraft engineering for inspection of aircraft in flight andin the course of ground inspection and testing of the strengthcharacteristics; in general engineering for inspection and testing ofcranes, pressure vessels and other metal structures; in construction forquality control and inspection of bridges, towers and masts.

The suggested frequency of clock pulses is 0.5-2.0 MHz. The duration ofclock pulses and time marker signals should be 100-200 μs.

It is also expedient that the digit capacity of the counters in the timeinterval measurement units 5, as well as of the counter in the unit 6measuring the parameters of acoustic signals should be sixteen bits, andthe word digit capacity of the voltage-to-code converter in the unit 6measuring the parameters of acoustic emission signals should be twelvebits.

We claim:
 1. An apparatus for acoustic-emission inspection of articles,comprising: channels each including a series connection of a transducerof acoustic emission signals, positionable on an article underinspection, and an amplifier of electric signals, having an outputconnected to a shaper of single pulses and to a unit for measuringparameters of acoustic emission signals, and also a clock pulsegenerator connected with each channel, a switching unit having inputsconnected to outputs of the units for measuring the parameters ofacoustic emission signals and also connected with the shapers of singlepulses of respective channels, and a computer for processingacoustic-emission data, connected to the switching unit, furthercomprising, in each channel, a unit for measuring time intervals, havinga first input connected to an output of the shaper of single pulses, asecond input connected to an output of the clock pulse generator, and anoutput connected to the input of the switching unit, and also afrequency divider having an input connected to the output of the clockpulse generator and an output connected to the switching unit, and an ORgate having inputs in a number equalling the number of the channels,said inputs of said OR gate being connected to the respective outputs ofthe shapers of single pulses of each channel, and having an outputconnected to third inputs of the respective units for measuring timeintervals in each channel.
 2. An apparatus according to claim 1, furthercomprising: an additional unit for measuring time intervals, having afirst input connected to an output of the frequency divider and to anadditional input of the OR gate, a second input connected to the outputof the clock pulse generator, a third input connected to the output ofthe OR gate, and an output connected to the input of the switching unit.